This invention relates to a system for the destruction of organic waste material and more particularly it relates to a process for the destruction of organic waste material which may or may not contain polyhalogenated waste material, and to apparatus for carrying out the process.
It is known to destroy halogenated organic waste material by reduction procedures using, for example, sodium metal or sodium napthalide. It is also known to destroy halogenated organic waste material by oxidation, using, for example, high temperature incineration. These known processes have certain limitations or disadvantages in that they can only be used for particular kinds of waste material. Moreover, the chemical reagents used for the destruction are sometimes hazardous to handle and the destruction may lead to the formation of highly toxic by-products.
The dimensions of the problem relating to the disposal of polyhalogenated liquids, particularly polychlorinated biphenyls (known generally, and to the public as PCBs) and associated wastes have been reviewed in the Environment Canada Economic and Technical Review Report EPS 3-EC-83-1. Bearing in mind the suspected carcinogenic nature of PCBs and the apparent absence of degradation in nature, over extremely long time periods, the identified quantities of PCBs presently in use in electrical transformers and capacitors (Table 7 of the Report), comprising a mass value of 14.8 million kilograms, conveys some idea of the scale of the problem.
Furthermore, the accumulation of these materials in numerous localities, mostly remote from the existing large-scale incinerators available in the U.S. and Canada for disposal purposes further emphasizes the extreme nature of the problem. Public awareness to the potential danger of PCBs to public health also further complicates the situation in precluding transportation thereof to existing combustion facilities. The occurrence of certain, well-publicized, PCB spills has further exacerbated this aspect of the problem.
The existing method of disposing of these types of substance has been by incineration, in large installations. While claims have been made to the achievement of very high percentile effectiveness of disposal by this method, there is concern that the reports may prove less than valid, on a long-term, continuing basis. In addition incineration or oxidation will form highly toxic by-products such as chlorinated dioxins if operated outside of exact optimal temperatures and residence time requirements.
One identified problem, referred to at Page 28 of the above-noted Report, which contributed to the demise of the related PCB incinerator, was the formation of a ring of "agglomerated material" during incineration. This type of "glop" formation may well be a characteristic by-product of incineration systems, and possibly is indicative of partial recombinations of molecules into ring compounds of a suspect type. This constitutes a further reason for providing a changed process.
Pyrolysis or starved air thermal destruction or degradation of solid and liquid organic waste products of hydrocarbons has previously been hampered by the formation of tars and polynuclear aromatic hydrocarbons containing from one to five aromatic rings. This invention includes the addition of gaseous reducing agents, particularly hydrogen, in concentrations sufficient to saturate or reduce the molecules produced such that polyaromatic structures are eliminated as by-products of the intended reaction.